First of all isn't it La Poste in Geneva

Have you signed up for the Post's e-service online. One of the advantages is they send you notifications (email/sms/notifications if you install the app on your smartphone) at 7am when your package is arriving the same day with an estimate.

Secondly you get a ping as soon as the Postie is entering in the handheld they have that you're not ostensibly there, potentially allowing you to react in situ.

I've often popped outside when I'm not supposed to be inside simply as the wrong bell was pushed (I know, non-Swiss names are so difficult) after the App told me attempted delivery had ostensibly failed.

Can you see the Postvan when it's in your street? I usually see it on days I'm expecting a delivery and proactively go outside to engage directly with my trusty carrier.

It may just be that La Poste are outsourcing deliveries to "a man with a van" with a small "La Poste" sign in their windscreen which you can't easily spot, and let's just say, your mileage may vary.....